The Group of 20 advanced and emerging countries has not enacted the policies needed to reach its growth targets, Australian Prime Minister Tony Abbott said on Thursday, casting fresh doubt on the ambitious roadmap laid out by the group earlier this year.

Abbott told a meeting of the Business 20 leaders in Sydney on Thursday that member countries would fall short by as much as half of their goal of raising collective GDP by an additional 2 percent over five years if they did not take stronger measures.

Abbott said the growth strategies of individual countries are taking shape following that pledge from G20 Finance Ministers at a meeting in Sydney in February.

"They contain several hundred proposed measures - but quantity does not always mean quality," he said at the opening of the B20 summit.

Australian Treasurer Joe Hockey has previously chided the group for its progress in meeting economic growth targets set by the Group, calling it "unacceptable" that only "one-tenth" of the necessary work had been achieved by April of this year.

G20 members represent around 80 percent of global gross domestic product, more than 75 percent of global trade, and two-thirds of the world's population.

Australia, which has the rotating chair of the G20 this year, is hoping a tight focus for the cumbersome grouping will refute criticisms of lots of talk and little action. It is expected to focus on measures such as boosting infrastructure spending and fiscal discipline to achieve the growth target.

Abbott said G20 leaders will produce a short, three-page communique in "plain language" when they meet in Brisbane in November.

"Australia's task is to keep the G20 totally focused on economic growth and to resist the temptation to deal with every ill that the world may face," Abbott said.

The B20, set up in 2010 to give policy recommendations on behalf of the international business community to the G20, says addressing a $57 trillion shortfall in global infrastructure through to 2030 will be crucial in meeting this goal.

But the group has criticised cumbersome global rules and long delays to approval processes that make it hard for large pension funds and insurance companies to invest in major infrastructure projects.

Abbott is supportive of the infrastructure goal, saying Australia is leading by example, investing A$50 billion ($46.8 billion) in a rolling 15-year list of infrastructure priorities.

But he is also stressing fiscal discipline. His Conservative-led Coalition government delivered a tough budget earlier this year and is scrapping controversial taxes on carbon and mining as it tackles what is says are unsustainable deficits due to total A$60 billion over the next four years.

"We really are at the limits of what macro measures can do to drive growth," Abbott said. "We need to manage the exit from unconventional monetary policy and to restore government's fiscal position to sustainability."

Abbott was also receptive to lobbying by the G20 to reduce financial regulation, which Australia and New Zealand Banking Group CEO Michael Smith said on Wednesday was deterring infrastructure investment and limiting the provision of trade finance.

"We need to unshackle business by reducing regulation and by accepting that some risk is unavoidable," Abbott said.